State the application's broad, long-term objectives and specific aims, making reference to the health relatedness of the project. Describe concisely the research design and methods for achieving these goals. Avoid summaries of past accomplishments and the use of the first person. This abstract is meant to serve as a succinct and accurate description of the proposed work when separated from the application. If the application is funded, this description, as is, will become public information. Therefore, do not include proprietary/confidential information. The PITX2 transcription factor is essential for normal eye development in vertebrates. Mutations in PITX2 result in Axenfeld-Rieger syndrome (ARS) associated with developmental glaucoma and other systemic defects. Our studies demonstrate conservation of the role of pitx2 in zebrafish ocular development. Using zebrafish model, we identified multiple regulatory regions mediating PITX2/pitx2 expression during eye, brain and craniofacial development. These studies led to the discovery of a novel mechanism of Axenfeld-Rieger syndrome: the deletion of the distant regulatory elements upstream of PITX2. In fact, using a large cohort of ARS patients we showed that virtually all classic ARS cases can be explained by nucleotide or copy number mutations in PITX2 when both coding and regulatory regions are examined. Further exploration of the identified regulatory sequences resulted in tentative identification of upstream regulators of PITX2/pitx2 that are currently being analyzed in terms of their role in normal ocular development and disease. Several downstream genes have also been identified and verified by in vitro and in vivo assays. The genes identified by us and some additional published factors will be further evaluated for their role in PITX2/pitx2 pathway in this application. One of the innovations of this proposal is that we plan to use the resources generated by us during the previous funding period in terms of pitx2 enhancer transgenic lines expressing GFP in periocular mesenchymal (POM) cells and pitx2 knockdown reagents to identify transcripts that distinguish normally differentiating and pitx2-deficient POM cells at different developing stages. This will result in robust in vivo identification of downstream effectors of PITX2/pitx2 as well as aid in general characterization of this migratory population with high significance to normal eye development. Another major innovation is our utilization of zinc finger nucleases- driven genome editing technology to generate pitx2 lines carrying mutations in pitx2 coding region (null allele) and CE4 regulatory element that has been previously shown to be involved in different aspects of pitx2 expression including strong presence in POM cells. Our main hypothesis is that PITX2/pitx2 is a conserved factor that is essential for inducing differentiation of periocular mesenchyme cells upon their migration into the anterior segment of the developing eye. Discovery of the upstream regulators of PITX2 expression and its downstream effectors will provide insight into the mechanisms of vertebrate embryonic eye development and are likely to identify new causes of human glaucoma phenotypes which can be further explored as potential therapeutic targets.